Fig. 1. Craniofacial dysmorphogenesis and skeletal abnormalities in Msx1/2 compound mutant mice. (A-E) Craniofacial morphology of control (A,C) and Msx1/2 double-mutant embryos (B,D,E) at E15.5. A and B show frontal views; C,D and E lateral views. Msx1^–/–; Msx2^–/– embryos exhibit exencephaly, a hypoplastic maxilla, cleft mandible, and defects in the fusion of the median lateral, nasal and maxillary prominences. Arrows in B, D and E indicate the whisker pad. (F-I) Alkaline phosphatase stain of coronal sections of control (F,H) and mutant (G,I) embryos. Boxed areas in F and G are enlarged in H and I. Msx1/2 mutants exhibit cleft palate (asterisk in G). Arrows in H and I indicate vibrissa follicles. Note, the mutant has divided whisker pads (brackets in I). (J-S) Skeletal analysis of Msx1/2 compound mutants. (J-Q) E18.5 Alizarin Red/Alcian Blue-stained bone and cartilage. (J,L,N,P) Normal controls; (K,M,O,Q) Msx1/2 mutants. (J,K,P,Q) Lateral views; (L,M) dorsal views; (N,O) ventral views. Note that a significant portion of the cranial skeletal components, including neural crest derivatives, is either missing or severely affected in mutant embryos. (P,Q) Fusion of hypoplastic mandible and maxilla is seen in the Msx1/2 mutant (Q). Note that tympanic ring was also hypoplastic in the mutant. (R,S) Lateral views of Alcian Blue-stained control (R) and Msx1/2 mutant (S) heads at E15.5. Note the parietal, supraoccipital and caudal processes of chondrocranium were absent in mutant. bo, basioccipital; bs, basisphenoid; c1, first cervical vertebra; e, eye; eo, exoccipital; fb, frontal bone; ip, interparietal bone; jg, jugal bone; ln, lateral nasal prominence; m, Meckel's cartilage; md, mandible; mn, median nasal prominence; mx, maxilla; na/nb, nasal bone; ns, nasal septum; oc, otic capsule; oe, outer ear; pb, parietal bone; pl, palatine; pmx, premaxilla; ps, palatal shelf; so, supraoccipital bone; sq, squamosal bone; t, tongue; tr, tympanic ring; ty, thyroid cartilage. Scale bars: 1 mm.